Method for cast molding plastic substrate

Abstract

A method for producing a plastic substrate having Tg of 110 DEG C. or more is disclosed, which comprises radical polymerizing a polyfunctional (meth)acrylate compound in a mold by a cast molding method, removing the resulting substrate from the mold when the glass transition temperature of the substrate reaches 10 DEG to 100 DEG C., and then post-curing the substrate. The method of the present invention can provide high quality plastic substrates with high productivity.

What is claimed is: 
     
       1. A method for obtaining a molded transparent plastic substrate by radical polymerizing a polymerizable monomeric liquid composed of at least one polyfunctional (meth)acrylate compound, the polymerization reactions consisting essentially of radical polymerization reactions, any catalyst present being a radical initiator, by a cast molding method, wherein in a first step the final shape of the plastic substrate is obtained by radical polymerizing the polyfunctional (meth)acrylate compound under cast molding conditions in a mold until the glass transition temperature of the polymerizing composition reaches 10° to 100° C., in a second step the shaped substrate as obtained in the first step is removed from the mold and in a third step the substrate is post-cured free of the restraints of a mold to obtain a substrate having a glass transition temperature of 110° C. or more and having the shape imparted by the first step. 
     
     
       2. The method as claimed in claim 1, wherein the polyfunctional (meth)acrylate compound is a compound represented by the formula (I): ##STR2## wherein R 1  is an alcohol residue having 2 to 50 carbon atoms, R 2  is H or CH 3 , and n is an integer of 2 to 6. 
     
     
       3. A method for obtaining a molded transparent plastic substrate by radical polymerizing a polymerizable monomeric liquid composed of at least one polyfunctional (meth)acrylate compound alone or admixed with at most 10% of other radical polymerizable monomers, the polymerization reactions consisting essentially of radical polymerization reactions, any catalyst present being a radical initiator, by a cast molding method, wherein in a first step the final shape of the plastic substrate is obtained by radical polymerizing the polyfunctional (meth)acrylate compound under cast molding conditions in a mold until the glass transition temperature of the polymerizing composition reaches 10° to 100° , in a second step the shaped substrate as obtained in the first step is removed from the mold, and in a third step the substrate is post-cured at a temperature below 150° C. free of the restraints of a mold to obtain a substrate having a glass transition temperature of 110° C. or more, and this substrate is then further post-cured at a temperature of 150° C. or more, the shape of the final product being that imparted by the first step. 
     
     
       4. The method as claimed in claim 3, wherein the polyfunctional(meth)acrylate compound is a compound represented by the formula (I): ##STR3## wherein R 1  is an alcohol residue having 2 to 50 carbon atoms, R 2  is H or CH 3 , and n is an integer of 2 to 6. 
     
     
       5. The method as claimed in claim 3, wherein the radical polymerization in the mold is carried out by irradiation with ultraviolet rays. 
     
     
       6. The method according to claim 2 wherein the polyfunctional (meth)acrylate compound is admixed with at most 10% of other radical polymerizable monomers. 
     
     
       7. The method according to claim 4, wherein the polyfunctional (meth)acrylate compound is admixed with at most 10% of other radical polymerizable monomers. 
     
     
       8. The method as claimed in claim 2 wherein the monomeric liquid is composed of at least one polyfunctional (meth)acrylate compound alone. 
     
     
       9. The method as claimed in claim 5 wherein the monomeric liquid is composed of at least one polyfunctional (methy)acrylate compound alone and the transparent substrate is a disc substrate for optical discs or magneto optical discs.